As is known, the filtering of air in the motoring or industrial field is generally obtained by means of a filter group which comprises an external casing provided with an inlet for fluid to be filtered and an outlet of filtered fluid, and a filtering cartridge suitable for defining a chamber, for example external, communicating with the inlet of the fluid to be filtered.
In this way, the fluid that flows from the inlet towards the outlet of the filter is forced to cross the filter membrane which retains the impurities possibly present therein.
A typical filter cartridge comprises a tubular filter membrane and two support plates, upper and lower, which are fixed to the opposite ends of the filter membrane.
At least one of the support plates is commonly provided with a central opening, aligned with the longitudinal axis of the filter membrane, through which the internal volume of the filter membrane is placed in communication with the inlet of the fluid to be filtered, in a case in which the filter membrane is configured such as to be crossed from inside towards outside, or with the outlet of the fluid, to be filtered, in a case in which the filter membrane is configured such as to be crossed from outside towards inside.
The casing, in these types of air filters, generally comprises a support body, conformed as a flange (or plate), provided with a hole defining the outlet and set in communication with the internal chamber of the filter membrane.
As is known, due to the high flow rate of air to be subjected to filtering for this type of filter group, the filter cartridge must necessarily exhibit considerable dimensions, at least such as to enable passage of the air without exceeding certain values as set by the norms and standards in the sector, which for example impose low load loss values.
Because of the significant dimensions of the filter cartridge, the installation and replacement thereof in these applications can represent a problem connected to the step of moving and manoeuvring it.
In an attempt to alleviate the work of the personnel specialised in installing the filter cartridge, the prior art provides various solutions for removably engaging the filter cartridge to the casing (for example to a cover of a beaker body or a support plate).
A first type of these solutions comprises the use of a bayonet-type engagement: these types of engagements comprise at least two profiled protrusions defined in the filter cartridge, each of which is destined to be inserted in a special groove realised in the support flange, such that the engagement is enacted by a short axial translation of the filter cartridge towards the support flange and a consequently small rotation about the axis of the filter cartridge.
These bayonet couplings, however, exhibit some drawbacks due mainly to the required complexity of the engagement.
It is usually necessary to provide means for blocking the reciprocal rotation between the filter cartridge and the support flange (or casing), which are for example flexible devices, grooves with labyrinthine profiles or threaded organs.
These blocking systems are on the one hand not particularly reliable and not very resistant over time, especially after repeated replacements of the filter cartridge, and on the other hand they lead to an increase in production costs of the filter cartridge and the casing (support flange) as well as costs over time for maintenance operations for replacing the filter cartridge.
A second known type of engagement, alternative to the above-described bayonet couplings, comprises axial snap-engagements, which are however not used in air filter groups, where there are high flow rates of air to be filtered, as the weight and large dimensions of the filter cartridges would made the exact positioning of the engaging means difficult to assess.
Further, the need to ensure engaging of a filter cartridge of considerable weight would necessarily lead to realising an axial snap-fit that would be hard to remove.